Certain electrocardiographic findings are described in 30 necropsy patients with clinically isolated pure, chronic, severe aortic regurgitation. They were 19 to 65 years old (mean 45). The hearts of the 22 men ranged in weight from 430 to 1,110 g (mean 717) and of the 8 women, from 375 to 950 g (mean 638). Four had grossly visible left entricular (LV) scars. All but 1 patient was in sinus rhythm. The PR interval was greater than 0.20 second in 8 patients (28%) and the QRS duration ws greater then 0.12 second in 6 patients (20%). Only 5 patients (17%) had 1 or more ventricular premature complexes recorded on the resting electrocardiogram analyzed. The mean QRS amplitude for each of the 12 leads average 23 mm. The highest mean QRS voltage occured in leads V2 and V3 (each 38 mm), and the lowest in lead aVR (11 mm). The mean QRS voltage in V5 was higher than V6 (33 vs 28 mm) and in 22 patients (73%) the QRS voltage in V5 was higher than in V6. The sum of the S wave in V1 plus the larger of the R wave in V5 or V6 (Sokolow-Lyon index) averaged 51 mm and in only 22 patients (73) was it greater than 35 mm.